1. Field of the Invention
The present invention relates to a process for producing a flexible polyurethane foam through reaction of a polyol and a polyisocyanate in the presence of an amine catalyst, a blowing agent, and a foam stabilizer. More particularly, the present invention relates to a process for producing a flexible polyurethane foam having high air flow from a formulation employing, as the blowing agent, a decreased amount of a halogenated hydrocarbon and an increased amount of water.
2. Description of the Related Art
Flexible polyurethane foams are widely used for producing vehicle parts, furniture, bedding, cushions, and the like. Hot mold foams and cold cure mold foams, out of the flexible polyurethane foams, are widely used mainly for seat cushions for automobiles.
Generally, a hot mold foam is produced by mixing a starting liquid formulation for polyurethane composed of a polyisocyanate and a polyol containing an amine catalyst, an organometallic catalyst, a blowing agent, a foam stabilizer, and other auxiliary, then foaming the mixture in a mold kept at 30.degree. to 40.degree. C., post-curing it in an oven, and releasing it from the mold. Conventionally, a halogenated hydrocarbon and water are employed as the blowing agent for the hot mold foam. Usual formulation for hot mold foams for front backs and rear backs of automobiles employs from 2.0 to 4.5 parts by weight of water and from 5 to 10 parts by weight of a halogenated hydrocarbon such as CFC-11 based on 100 parts by weight of the polyol, as blowing agents.
A cold cure mold foam, which is generally called "HR foam", is produced without conducting post cure in an oven owing to the use of a highly reactive polyol. For such kinds of foams, a halogenated hydrocarbon is used to produce foams of low density and low hardness.
Recently, among the halogenated hydrocarbons, chlorofluoro carbons (CFCs) such as CFC-11 are indicated to destroy the ozone layer, so that the use of CFCs has come to be regulated and is required to be reduced throughout the world. Consequently, various investigations are being made to develop a formulation employing less CFC-11 and more water instead as the blowing agent in conventional flexible foam formulations. For the same purpose, elevation of the mold temperature up to 50.degree. to 60.degree. C. is also being investigated to raise the foaming efficiency.
In the production of flexible foam, however, decrease of CFC-11, increase of water, or elevation of the mold temperature disadvantageously results in rise of foam hardness, liability of giving splits in the interior of the foam, or roughening of cells at the surface of the foamed article. For the purpose of solving such problems, Japanese Patent Publication No. Sho 62-21807, and Japanese Patent Laid-Open Nos. Hei 1-259022 and Hei 2-20251 disclose increase of ethylene oxide content and increase of terminal oxyethylene groups to lower the hardness of foams, and Japanese Patent Laid-Open No. Hei 1-266121 discloses increase of an organotin catalyst and use of a higher potency foam stabilizer to improve high-temperature moldability.
However, the use of a highly reactive polyol having an increased terminal oxyethylene group, the increase of organotin catalyst or the use of a higher potency foam stabilizer will disadvantageously cause increase of the ratio of closed cells in the foam, which impairs remarkably the air flow of the foam, or may cause shrinkage of the foam.
A possible method for improving the air flow of the foam is to use, as the amine catalyst, triethylenediamine, bis(dimethylaminoethyl) ether, N-ethylmorpholine, or the like. However, the use of such an amine catalyst narrows the processing latitude, and causes the serious problem of splitting, giving no satisfactory physical properties of the foam.
Accordingly, an improved formulation for flexible polyurethane foams is desired which contains less CFC-11 and more water as the foaming agent, yet giving high moldability and high air flow.
The inventors of the present invention made comprehensive investigation from the above viewpoint regarding the catalyst in the flexible polyurethane foam formulation, regarding the catalyst in the formulation employing an increased amount of water with a highly reactive polyol having an increased amount of a terminal oxyethylene group, and found a novel fact that use of an amine having a specific chemical structure as the catalyst enables production of a flexible polyurethane foam having high air flow with improved moldability of the foam, and completed the present invention.